BC857: Overview,Specifications,Main uses,Features,application fields,working principle and alternative models


BC857 Overview:

The BC857 is a general-purpose PNP bipolar junction transistor (BJT) known for its low noise characteristics and high current gain. It is commonly used in a variety of electronic circuits for amplification and switching purposes. Here is an overview of the BC857 transistor, including its specifications, main uses, features, application fields, working principle, and alternative models:



  • Type: PNP Bipolar Junction Transistor (BJT)
  • Package: SOT-23 or similar
  • Collector-Base Voltage (VCBO): Typically around 50V
  • Collector-Emitter Voltage (VCEO): Approximately 45V
  • Emitter-Base Voltage (VEBO): Around 5V
  • Collector Current (IC): Typically 100 mA
  • Power Dissipation (Pd): Varies with operating conditions
  • Transition Frequency (fT): Depending on model, typically in the range of tens to hundreds of megahertz
  • DataSheet

    BC857,215 PDF

Main Uses:

  • Amplification: Commonly used in audio amplifiers, signal processing circuits, and low-noise amplifier applications.
  • Switching: Utilized in electronic switches, low-power control circuits, and digital logic circuits.
  • Buffering: Used as input and output stages in communication circuits.
  • Voltage Regulation: Integrated into voltage regulator circuits for precise voltage control.


  • Low Noise: Known for its low noise characteristics, suitable for high-fidelity audio applications.
  • High Current Gain: Offers high current gain (hFE) for efficient amplification.
  • Compact Package: Available in compact surface-mount packages like SOT-23 for easy integration.
  • General-Purpose: Versatile transistor suitable for a wide range of electronic applications.
  • Medium Power: Capable of handling moderate power levels depending on the operating conditions.

Application Fields:

  • Audio Electronics: Used in audio amplifiers, preamplifiers, and equalizer circuits.
  • Signal Processing: Integrated into signal processing circuits for amplification and filtering.
  • Telecommunication: Found in communication devices, telecommunication systems, and radio-frequency circuits.
  • Consumer Electronics: Applied in various consumer electronic products for amplification and control purposes.

Working Principle:

  • In an amplification circuit, the BC857 amplifies input signals with the help of appropriate biasing.
  • When used as a switch, the transistor controls the flow of current based on its base voltage.
  • By configuring the biasing correctly, the transistor can perform the desired function like amplification or switching.

Alternative Models:

  • BC557: NPN counterpart of BC857, commonly used in complementary configurations.
  • 2N3906: PNP transistor with similar characteristics and applications.
  • BC327: Another PNP transistor with comparable specifications and features.


  • The BC857 is a versatile and widely used transistor in various electronic circuits due to its low noise, high gain, and moderate power handling capabilities.
  • When selecting an alternative transistor, consider compatibility, voltage and current ratings, and overall specifications required for the specific application.

The BC857 PNP transistor is a reliable component suitable for applications requiring low noise amplification, high current gain, and moderate power handling, commonly used in audio electronics, signal processing circuits, and telecommunications applications for efficient amplification and switching operations.